1. Technical Field
This invention relates to a holding structure for a touch panel, which is provided to a display or an operation unit of a variety of electronic devices and being used as an input device.
2. Description of the Related Art
Conventionally, electronic devices having a touch panel function as input means at the display surface have been used widely. One of the structures of the touch panels was a resistance-sensitive type. In the resistance-sensitive touch panel, usually a transparent ITO (indium oxide) film is formed on the glass surface of the touch panel in a predetermined pattern. Electrodes are connected to the end portion of the ITO film and the peripheral edge is coated by overcoating. And dot spacers are provided between the upper and lower panel substrates both on which ITO films are deposited. When an operator presses the surface of the touch panel, the ITO films on the upper and lower panels get in contact with each other. The pressed position on the panel is detected in accordance with the resistance value at that time.
In the touch panel device, as it is disclosed in Japanese Patent Application Publication No. 07-105781, the touch panel and the front surface of the liquid crystal display panel or the like are applied to each other at the entire surface using a transparent acrylic adhesive. In this way, by eliminating the interspace between the touch panel and the liquid crystal display panel, the Newton rings or the glare due to the distortion of the touch panel substrate during operation or the like are prevented from generation.
In addition, the touch panel device is disposed in pile on the liquid crystal display panel or the like, and an operator carries out the input operation by directly touching such display surface. Even though the ITO films on the upper and the lower panel substrates get in contact with each other when an operator presses the surface of the touch panel, the operator can neither feel nor be sure whether the contact is closed or not. And so, there is a touch panel with a so-called force feedback function which vibrates the touch panel by detecting the pressing operation and gives an operator an operation feeling. As it is shown in FIG. 8, the touch panel device equipped with the force feedback function is applied, for example, to the display of handheld information equipment or the like, and is composed of the liquid crystal panel 2 and the touch panel 4 being accommodated in the casing 6 made of resin or the like. Piezoelectric devices 3 for the force feedback function are equipped at the side edge of the touch panel 4. And elastic supporting portions 5 made of rubber or the like are provided at the four corners between the liquid crystal panel 2 and the touch panel 4 in the casing 6. The elastic supporting portions absorb the vibration of the touch panel 4 due to the piezoelectric devices 3 and hold the touch panel 4.
In addition, as it is shown in FIG. 8, in order to enhance the dust-proof feature and the visual design, in some touch panels, a transparent protective sheet 7 is disposed on the outer front surface of the touch panel 4. The protective sheet 7 is applied in order to cover simultaneously the touch panel 4 and the opening 6a of the casing 6. As it is shown in FIG. 9 and FIG. 10, the protective sheet 7 is bonded to the front surface of the touch panel 4 with a transparent acrylic adhesive 8 or the like being applied on the entire front surface of the touch panel 4. Moreover, as it is shown in FIG. 11, the peripheral edge of the protective sheet 7 is bonded with the opening peripheral edge 6b being the periphery of the opening 6a of the casing 6 at the entire corresponding peripheral surface by the adhesive 9.
In the case of the holding structure for a touch panel described in the related art mentioned above, since the protective sheet 7 is applied to the touch panel 4 on the entire front surface, there was a problem that the vibration of the touch panel 4 was restricted, the vibration amplitude became smaller and the damping appeared fast, so that the sufficient force feedback function could not be demonstrated because of the bonding with the protective sheet 7 when the piezoelectric devices 3 vibrated in order to demonstrate the force feedback function due to the piezoelectric devices 3. Similarly, because the peripheral edge of the protective sheet 7 was bonded with the opening peripheral edge 6b of the casing 6 at the entire corresponding peripheral surface, this made the vibration due to the piezoelectric devices 3 absorbed and damped so that the force feedback function was diminished.